Share a multiple-choice question about variables (including global variables, local variables, the scope of variables, and life cycle knowledge points)

Catalog

1. subject

2. Topic analysis

3. Question answer

4. Topic knowledge

4.1 Local variable and global variable

4.2 Scope of variable 、 Life cycle

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Recommended reading order :

1. subject ->3. answer ->2. Topic analysis ->4. Topic knowledge

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1. subject

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1、 Perform the following procedure , The correct output is （ ）

#include<stdio.h>
int x=5,y=7;
void swap()
{
int z;
z=x;
x=y;
y=z;
}
int main()
{
int x=3,y=8; 
swap();
printf("%d,%d\n",x, y);
return 0;
}

A: 5,7         B: 7,5         C: 3,8         D: 8,3

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2. Topic analysis

This is a typical study of global variables 、 Local variables and the scope and life cycle of variables .

It's better to watch by number

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3. Question answer

        C：3,8

4. Topic knowledge

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4.1 Local variable and global variable

In the same range , Local variable names cannot be the same , Cannot be defined repeatedly .

When a local variable has the same name as a global variable , Local variables take precedence .

It is recommended not to name global variables and local variables the same .

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4.2 Scope of variable 、 Life cycle

Scope

Scope （scope） It's a programming concept , Generally speaking , The names used in a program are not always valid / Usable , The scope of the code that defines the usability of the name is the scope of the name . In a popular sense , Where does this variable work , Where is its scope .

1. The scope of a local variable is the local scope of the variable .

The demonstration is as follows ：

 2. The scope of global variables is the whole project .

 

Life cycle

The life cycle of a variable is the period between the creation of a variable and its destruction .

1. The life cycle of a local variable is ： Enter the scope lifecycle begins , Out of scope life cycle ends .

2. The life cycle of global variables is ： The whole life cycle of the program .